The present invention relates to a barrier structure for food packages which is useful for providing an extended package and product shelf life. The barrier structure of the present invention may be used in a variety of packages, including paper cartons. The barrier structure for the food package of the present invention is heat sealable, thus providing a useful barrier structure for converting a stock material into cartons and similar food retaining packages which require heat sealing. The barrier structure of the present invention is particularly useful in packaging orange juice and similar citrus products.
With respect to juice containers, fruit juice manufacturers and packaging suppliers must address a variety of performance considerations in order to provide a cost effective container which meets the needs of multiple performance characteristics. In recent years, there has been much attention focused on providing oxygen barriers for the container to avoid the oxidation of flavoring components found in the juice along with the oxidation loss of L-ascorbic acid (vitamin C). As various packaging innovations have been developed which lead to the improved retention of nutrients and taste, the packaging shelf life has correspondingly been increased. As a result, as the useful packaging shelf life has increased, the durability and longevity of the packaging has become an increased issue.
One aspect of shelf life with regard to paperboard containers as are commonly used for milk, orange juice, and similar products involves the tendency of the carton structure to distort or bulge over time. The carton bulge is unsightly and may be mistakenly perceived by consumers as indicative of an expired or spoiled product.
Heretofore, it was widely held that the bulge properties of cartons were best controlled by increasing the thickness or stiffness of the underlying paperboard substrate. In accordance with the present invention, it has been found by applicants that by reducing the moisture transmission rate, particularly moisture passing through the interior surface of a sealed carton, offers significant improvements in the bulge properties of the carton. Further, it is possible to provide a carton having a highly effective oxygen barrier layer which, in combination with the water vapor barrier, provides a cost effective desirable carton for use with juice, citrus products, milk, and other high liquid content food products.
A variety of barrier structures and food packages are known within the art.
For instance, U.S. Pat. No. 4,753,832 is directed to a barrier laminate suitable for citrus beverages which has an innermost beverage contacting surface comprising a thin layer of glycol-modified polyethylene terephthalate (PET-G) which provides improved oxygen barrier properties as opposed to an uncoated substrate.
U.S. Pat. No. 4,513,036, which is incorporated herein by reference, discloses a barrier laminate applied to a paperboard substrate comprising a web of propylene polymer adjacent to a food contact layer of an olefin polymer. An outer surface of the paperboard substrate is coated with a layer of a heat sealable olefin polymer. The structure sets forth a laminate having improved properties in retaining d-limonene along with improved retention of vitamin C levels.
U.S. Pat. No. 4,977,004, incorporated herein by reference, discloses a barrier liner for food packages comprising twin layers of ethylene-vinyl alcohol copolymers (EVOH). One layer is interposed between two moisture barriers such as high density polyethylene (HDPE), EVOH compatible adhesives, or low density polyethylene (LDPE). The innermost layer of EVOH provides a solvent barrier against loss of flavor components while the second EVOH layer serves as an oxygen barrier.
While there are a variety of barrier laminates directed to imparting protective properties for preventing loss of flavoring components, vitamin C, and barriers to reduce oxygen transmission through the laminate, there remains room for variation and improvement within the art.
The present invention provides a barrier structure suitable for converting into packages for foods and beverages which are economical, have good heat-sealing properties, exhibit low oxygen and water vapor permeability, and provide protection against carton bulge or creep.
In its broadest embodiment, the barrier structure of the present invention comprises a food contact layer or xe2x80x9cskin coatxe2x80x9d of a medium density polyethylene (MDPE) in which the MDPE is attached by an adhesive tie layer to a polyamide barrier layer. The polyamide barrier layer is attached directly along one surface to an inner paperboard surface. The polyamide layer and adjacent tie layer offer useful oxygen and water vapor barriers respectively. The MDPE skin coat provides an additional water vapor barrier and which further provides an essential oil barrier which reduces scalping, i.e., the absorption of d-limonene by the interior board coating.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.